High conductivity bare aluminum finstock and related process

ABSTRACT

A process for making aluminum alloy finstock having improved combinations of post-braze tensile strength, electrical conductivity and self-corrosion resistance. The process includes continuously casting into sheet an alloy composition. The composition includes about 0.35-0.60 wt. % Si, about 1.8-2.6 wt. % Fe, about 0.02-0.30 wt. % Cu, about 0.40-0.70 wt. % Mn, up to about 3.0 wt. % Zn, up to about 0.05 wt. % In; up to about 0.05 wt. % Ti and up to about 0.2 wt. % Zr, the balance aluminum, incidental elements and impurities. The casting including a solidification rate of greater than about 200° C./sec. The sheet is then rolled to an intermediate anneal gauge and then annealed. The sheet is then cold rolled to a desired final gauge.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional PatentApplication No. 60/400,735, filed Aug. 1, 2002, which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an alloy composition and to amethod for fabricating finstock, more particularly, the inventionrelates to an aluminum alloy composition and method for fabrication offinstock for applications such as aluminum heat exchanger end uses.

[0004] 2. Description of Related Art

[0005] Bare finstock for brazed automotive aluminum heat exchangers istypically fabricated from 3XXX Series aluminum alloys such as AA3003aluminum, an Aluminum Association (“AA”) alloy designation. Afterbrazing, these alloys are characterized by relatively low thermalconductivity as measured by electrical conductivity (“EC”) because ofthe high level of manganese trapped in solid solution in these alloys.Since the fins of such heat exchangers need to conduct heat away fromthe fluid carrying tubes, the thermal conductivity of these fins willimpact the overall efficiency of the heat exchangers into which they areinstalled.

[0006] As heat exchanger fabricators endeavor to reduce the weight ofcomponents, downgauging of the tubes and fins becomes necessary. Givenexisting designs of automotive heat exchangers, downgauging the finrequires an increase in conductivity, while still maintaining someminimum level of post-braze strength and self-corrosion resistance, ifthe efficiency and lifetime of the component is not to be compromised.

[0007] In an effort to produce such finstock, compositions and processeshave been modified. A typical example of the foregoing is disclosed inU.S. Pat. Nos. 6,592,688, 6,165,291, 6,238,497, 5,217,547, U.S.Publication No. 2003/0015573 and European Application No. EP1156129.

[0008] U.S. Pat. No. 6,238,497 describes a method of producing a highconductivity finstock. The method includes steps of continuously castingan aluminum alloy strip, rolling the as-cast strip to an intermediategauge, annealing the intermediate gauge strip and then cold rolling tothe final gauge. The alloy contains in wt. %: 1.6 to 2.4% Fe, 0.7 to1.1% Si, 0.3 to 0.6% Mn, 0.3 to 2.0% Zn with 0.005 to 0.040% Tioptional. The solidification cooling rates specified in U.S. Pat. No.6,238,497 relate to continuous slab casting technologies as the initialstep in fabricating the finstock.

[0009] In U.S. Pat. No. 6,592,688 a high conductivity aluminum fin alloyis described as containing: 1.2 to 1.8% Fe, 0.7 to 0.95% Si, 0.3 to 0.5%Mn, 0.3 to 1.2% Zn with 0.005 to 0.02% Ti optional. The solidificationcooling rates described in this patent also relate to slab castingtechnologies.

[0010] U.S. Pat. No. 6,165,291 describes a process for fabricating analuminum alloy fin with high post-braze conductivity. The processinvolves continuous strip casting the aluminum alloy, rolling it to anintermediate gauge, annealing the intermediate gauge strip and then coldrolling to final gauge. The alloy contains 1.2 to 2.4% Fe, 0.5 to 1.1%Si, 0.3 to 0.6% Mn, 0 to 1.0% Zn with 0.005 to 0.040% Ti optional. Thepatent indicates that Si is instrumental in developing strength througha combination of particle strengthening and solid solution strengtheningand that below 0.5 wt. % Si there is insufficient Si for strengtheningpurposes. It is noted that the cooling rates described in this patentrelate to twin roll casting technologies of aluminum alloys. It isfurther noted that twin roll casting technologies have been employedwithin the aluminum industry for years to produce common finstock alloyssuch as AA3003.

[0011] In view of the foregoing, there is a need for producing lighterweight finstock with efficient post-braze strength, conductivity andcorrosion resistance.

SUMMARY OF THE INVENTION

[0012] Generally, the present invention is an aluminum alloy finstockcomposition that achieves improved post-braze strengths by a combinationof particle and solute strengthening. In doing so, the present inventioncan achieve an attractive combination of post-braze ultimate tensilestrength (“UTS”) of roughly about 125 MPa, with electrical conductivityvalues of about 48% IACS or greater and with good self-corrosionresistance. One preferred range for this alloy composition, suitable fora controlled atmosphere brazing (“CAB”) with conventional fluxes thatare not magnesium tolerant include: about 0.35-0.60 wt. % Si; about1.8-2.6 wt. % Fe; about 0.02-0.30 wt. % Cu; about 0.40-0.70 wt. % Mn; upto about 3.0 wt. % Zn; up to about 0.05 wt. % In; and up to about 0.05wt. % Ti, the balance being aluminum, incidental elements andimpurities. The alloy may also include up to about 0.20 wt. % Zr; about0.05 wt. % or less Mg and about 0.05 wt. % or less Ni. Preferably, thealloy includes 0.35-0.5 wt. % Si, more preferably about 0.35-0.45 wt. %Si. The alloy also preferably includes about 1.8-2.4 wt. % Fe, about0.4-0.7% Mn, about 0.15-0.25 wt. % Cu, up to about 0.15 wt. % Zn andabout up to 0.03 wt. % In. When the alloy of the present invention isused in a controlled atmosphere braze with Mg tolerant fluxes, up toabout 0.3 wt. % Mg may be tolerated with the aforesaid elemental ranges.

[0013] The present invention is also directed to a process of makingaluminum alloy finstock having improved combinations of post-brazetensile strength, electrical conductivity and self-corrosion resistance.The process includes continuously casting into sheet an alloy with thecomposition described hereinabove into a sheet, rolling the sheet to anintermediate anneal gauge, annealing the rolled sheet, and cold rollingto a final desired gauge.

[0014] Continuous casting of the sheet may be performed with a twin rollcaster under rapidly cooling casting conditions that substantially avoidthe formation of primary intermetallic solidification compounds andproduces a sheet of thickness of about 2.0-10.0 mm, preferably about 6.0mm. The casting may be performed with a high speed sheet or belt casterthat freezes from at least one surface to substantially avoid formationof primary intermetallic solidification compounds.

[0015] The step of rolling the sheet to an intermediate anneal gauge mayinclude more than one intermediate thermal operation at either castgauge or after some initial cold reduction. The thermal operation mayinclude a 1-10 hour soak, preferably 1-8 hour soak, at a temperaturerange of about 320-450° C. Rolling may include both hot or warm rollingand cold rolling.

[0016] The rolled sheet may be annealed at a temperature below about450° C. The step of cold rolling to a final gauge may produce less thanor equal to about 50% reduction in sheet thickness.

[0017] The finstock alloy of the present invention provides enhancedpost-braze conductivity of about 48% IACS or greater as compared to itsAA3003 counterpart with values of about 41% IACS.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] When referring to any numerical range of values, such ranges areunderstood to include each and every number and/or fraction between thestated range minimum and maximum. A range of about 0.35-0.60 wt. %silicon, for example, would expressly include all intermediate values ofabout 0.36, 0.37, 0.38 and 0.40%, all the way up to and including 0.55,0.57 and 0.59% Si. The same applies to each other numerical property,relative thickness and/or elemental range set forth herein.

[0019] The present invention is an aluminum alloy finstock compositionthat achieves improved post-braze strengths by a combination of particleand solute strengthening. In one embodiment, the alloy includes about0.35-0.60 wt. % Si; about 1.8-2.6 wt. % Fe; about 0.02-0.30 Cu; about0.40-0.70 wt. % Mn; up to about 3.0 wt. % Zn and up to about 0.05 wt. %In; and up to about 0.05 wt. % Ti, the balance being aluminum,incidental elements and impurities. Preferably, the alloy includes0.35-0.5 wt. % Si, more preferably about 0.35-0.45 wt. % Si. The alloyalso preferably includes about 1.8-2.4 wt. % Fe, about 0.4-0.7% Mn,about 0.15-0.25 wt. % Cu, up to about 0.15 wt. % Zn and about up to 0.03wt. % In.

[0020] The alloy of the present invention includes about 0.35-0.60 wt. %Si, preferably 0.35-0.50 wt. % Si. Below 0.35 wt. % the strengtheningeffect of Si is expected to be minimal. Silicon contents greater than0.50 wt. % may not be necessary for the combinations of properties ofinterest.

[0021] Iron is important in the formation of the small intermetallicparticles during solidification. These particles are important forpost-braze dispersion strengthening and for influencing the post-brazegrain size. The Fe range is set at about 1.8-2.6 wt. %, preferably about1.8-2.4 wt. %. Below 1.8 wt. % the strengthening effect is insufficient,whereas, above 2.6 wt. % it is difficult to cast the alloy withoutformation of coarse intermetallic Fe-bearing particles that would createa problem during the fabrication of thin gauge finstock.

[0022] Manganese is important in modifying the Fe-bearing intermetallicparticles. Manganese will combine with the Fe and Si in theintermetallic particles and in so doing, increase the volume fraction ofparticles for strengthening. In addition, Mn will shift the corrosionpotential of the intermetallic particles to make it closer to thematrix, thus reducing the self-corrosion rate. Finally, Mn in solutioncan contribute to solid solution strengthening, although at thedetriment of conductivity. For these reasons, Mn is set to the range ofabout 0.40-0.70 wt. %. Below 0.40% the beneficial attributes of Mn arenot fully realized, whereas, above 0.70% Mn the post-braze conductivityof the alloy is notably reduced.

[0023] Copper is important for solute strengthening. While copper isoften avoided as an alloy addition to finstock for its effect oncorrosion, the unexpected results of the present invention show that atthe levels of Cu explored the self-corrosion rate of these alloys didnot notably increase, whereas the post-braze strength was improved. Forthat reason, the range of Cu addition is set at 0.02-0.30 wt. %.

[0024] Zinc, if present, is added for purposes of making a fin lessnoble than the tube to which it is brazed thereby affording cathodicprotection to the tube. Experimental work has also indicated that the Znis providing some additional solute strengthening. It has been observedthat additions of zinc of greater than about 2.0 wt. % are generally notdesirable. Such additions have a detrimental influence on conductivityand self-corrosion rates. In some instances, though, it may be necessaryto sacrifice those properties to allow for sufficient cathodicprotection of the tube. The maximum Zn limit of up to about 3.0 wt. %for this invention was established with that potential compromise inmind.

[0025] Indium is also a potential addition to shift the corrosionpotential of the fin. Additions of about 0.017 wt. % In were foundeffective in combination with Zn additions to shift the potential withminimal influence on conductivity. In laboratory work, additions of0.078 wt. % were found to result in notable increased self-corrosionrates so a range of 0-0.05 wt. % indium is established for this alloy.These additions are envisioned to be effective either without Znadditions or in combination with Zn additions.

[0026] Titanium is present for purposes of grain refinement duringcasting. For this reason Ti levels of up 0.05 wt. % are useful.

[0027] Zirconium, may be included for controlling the post-braze grainsize and shape. However, it has a negative impact on conductivity. Forthis reason, Zr may not be present in the alloy, but additions of up to0.2 wt. % are tolerable.

[0028] Magnesium is known to be an effective element from astrengthening standpoint. In alloys containing Si or where Si will bepresent due to diffusion from the Al—Si braze alloy during brazing, Mgcan contribute to strengthening through precipitation hardening byMg₂Si. Magnesium is preferably not present in CAB brazing alloys due tothe detrimental influence of Mg on brazeability when using popularcommercial fluxes (such as Nocolok®). Nevertheless, fluxes are beingdeveloped that are more tolerant of Mg and so the Mg limits for thisalloy are set at 0-0.3 wt. %. For better CAB “braze-ability” with aconventional brazing flux, magnesium contents are kept purposefully low,less than about 0.05 wt. %. When a magnesium-tolerant flux is used,however, higher Mg levels of up to about 0.3 wt. % may be considered foradditional strengthening. Such Mg amounts should be able to combine withthe Si in solution after brazing to precipitate a Mg₂Si strengtheningphase. In so doing, high conductivity is maintained by pulling the Mgand Si from solid solution.

[0029] The process of making the aluminum alloy finstock with theabove-described composition includes the steps of continuously castinginto a sheet, cold rolling, annealing and cold rolling the annealedsheet to a final gauge. Because of the high Fe content, the alloy of thepresent invention is preferably cast by a process that achieves veryhigh cooling rates (greater than about 200° C./sec) duringsolidification. Such high cooling rates assure the formation of smalldiameter intermetallic particles during freezing that fragment duringsubsequent thermo-mechanical processing, thus providing the largepopulation of very small particles for dispersion strengthening. Twinroll casting is particularly well suited for this purpose.Alternatively, casting can be performed on a high speed continuous beltcaster whose design affords high cooling rates. One such caster isdescribed in U.S. Pat. No. 5,564,491. “High speed belt casting”, as usedherein, refers to strip casting at speeds of greater than about 30meters/minute. Alternative casting methodologies that should alsosuffice include “melt drag casting” and most high speed, twin roll stripcasting processes that freeze the resultant strip product (from one orboth sides) with sufficiently high cooling rates during solidification.The high speed sheet or belt caster processes freeze from at least onesurface at rates sufficient to substantially avoid formation of primaryintermetallic solidification compounds. These rates are known by oneskilled in the art.

[0030] When the alloy of the present invention is twin roll cast tosheet, between about 2 to 8 mm thick, preferably it is cold rolled to anintermediate gauge in several rolling passes, annealed and then coldrolled to final gauge. For purposes of facilitating the cold rolling ofstrip, it may be advisable to include an additional intermediate thermaltreatment immediately after casting, or after some initial cold rollreduction. The thermal operation may include a 1-10 hour soak preferably1-8 hour soak at a temperature of about 320-450° C. or about 370-450° C.This can be followed by additional cold rolling to a second,intermediate gauge, annealing and then cold rolling to final gauge.Total cumulative thermal exposures during strip processing may belimited to minimize the coarsening of intermetallic particles.Typically, one intermediate anneal is preferred.

[0031] For the scenarios that involve casting alloy strip on a highspeed caster (either belt or twin roll), the initial rolling passes maybe accomplished by a combination of hot and warm rolling to intermediategauge after which an optional intermediate anneal may be appropriate.Thereafter, the sheet may be cold rolled to an inter-anneal gauge,before being annealed and cold rolled to final gauge. If the alloy ofthe present invention were to be cast on a melt drag apparatus, then thecoil of same preferably is cold rolled to an intermediate anneal gauge,annealed and cold rolled to final gauge.

[0032] Development work for this alloy utilized an apparatus thatchilled about 2 to 6 mm thick specimens of the alloy of the presentinvention from one side at approximately twin roll caster-type coolingrates. These chilled specimens were then machined, from one side, tomake pieces uniform in cross-sectional thickness. Those pieces were thencold rolled to an intermediate gauge (of about 81 microns), annealed forabout 1 hour at about 400° C., then cold rolled to about 63 microns forapproximating an H14-type temper. Table I below lists the compositionsof various alloys cast and processed in this along with finstockmaterials included for reference purposes. TABLE I Compositions SampleSi Fe Cu Mn Ni Zn In Ti Inventive alloys 1 0.42 2.06 0.14 0.44 0.0 0.630.0 0.015 2 0.42 2.02 0.22 0.45 0.0 0.63 0.0 0.015 3 0.43 2.06 0.19 0.450.0 0.00 0.0 0.016 4 0.42 2.03 0.16 0.45 0.0 1.66 0.0 0.016 5 0.44 2.000.18 0.44 0.0 2.62 0.0 0.016 6 0.42 2.00 0.18 0.43 0.0 0.68 0.0 0.025 70.45 2.20 0.20 0.45 0.0 0.75 0.017 0.024 Comparison alloys 8 0.43 2.110.0 0.44 0.0 0.64 0.0 0.014 9 0.44 1.58 0.0 0.48 0.0 0.65 0.0 0.017 100.42 1.78 0.0 0.54 0.0 0.66 0.0 0.016 11 0.45 2.00 0.19 0.44 0.0 4.200.0 0.016 12 0.91 1.6 0.0 0.62 0.59 0.66 0.0 0.015 13 0.88 1.56 0.0 0.470.0 0.64 0.0 0.015 14 0.90 1.81 0.0 0.54 0.0 0.65 0.0 0.015 15 0.6 0.70.05-0.20 1.0-1.5 0.1 max max max 16 0.46 1.9 0.02 0.01 1.2 1.2 0.01

[0033] Alloys 1-7 represent the compositions of alloys that are composedby the present invention and alloys 8-16 are the comparison alloys. Inparticular, alloy 15 represents the composition range for an AA3003alloy. Alloys 1-5 and 8-14 in Table 1 were processed using laboratoryequipment to an H14-type temper, then put through a thermal cycle thatsimulated a typical CAB braze cycle. That simulation included a 3 minutesoak at about 380° C., plus 9 minutes above about 590° C. with a peakmetal temperature of about 600° C.±5° C. Post-braze property assessmentsincluded: measuring tensile properties, electrical resistivity (whichwas then converted to % IACS conductivity values), metallographicallymeasured grain sizes and self-corrosion as measured by weight loss afterone week in a neutral salt spray environment per ASTM specificationB117, the disclosure of which is incorporated by reference herein. Postbraze solution potential was measured in accordance with ASTM G69 usinga saturated calomel electrode but the results were then converted forreference to a saturated AgCl/Ag electrode. The alloy 15 fin from Table1 was commercially available AA3003 finstock processed from twin rollcast stock. The alloy 16 fin was cast on a high speed belt caster andprocessed to fin by a combination of hot/warm and cold rolling with anintermediate anneal and cold rolling to final gauge. Both finstocks werethen subjected to the same braze cycle simulation and testing as per theother alloys of Table 1.

[0034] In another embodiment, inventive alloys 6 and 7 were cast on acommercial twin roll caster. The alloys were cast at about 5.59 mmthickness. Microstructural evaluation of the cast sheet indicated thecasting conditions used did not produce significant amounts ofcenterline segregation of intermetallic phases. In addition, theformation of coarse primary Fe-bearing intermetallic phases was largelyavoided. In the laboratory sections from these as-cast sheets wereprocessed to 50 micron finstock by cold rolling to the intermediateanneal gauge (71 microns), annealing the strips for about 4 hrs. atabout 400° C. and then cold rolling to 50 microns for an H14 temper.

[0035] The following Table II reports measured post-braze properties ofthese alloy compositions of Table I. TABLE II Post-Braze Properties Wt.Loss Sol. Po- UTS TYS E.C. Grain Size (mg/ tential vs. Alloy (MPa) (MPa)(% IACS) (microns) sq. cm) Ag/AgCl Inventive alloys 1 122.7 46.6 50.2283 0.24 −703 mV 2 124.6 47.5 49.2 357 0.23 −699 mV 3 118.6 45.3 50.6377 0.19 −688 mV 4 122.8 46.2 48.4 423 0.17 −794 mV 5 128.7 54.0 46.8391 0.32 −860 mV 6 117.2 46.5 50.8 1700 −713 mV 7 121.0 52.4 50.2 1285−741 mV Comparison alloys 8 112.7 44.4 50.1 700 0.20 −723 mV 9 107.542.0 50.1 725 0.21 10 113.2 44.1 49.2 772 0.20 11 133.8 52.2 44.2 2280.53 −900 mV 12 139.2 51.3 46.3 238 0.35 13 125.2 44.6 49.4 950 0.21−718 mV 14 126.6 47.7 49.2 840 0.19 −703 mV 15 111.0 47.6 41.8 0.22 16132.2 56.9 52.5 >10,000 0.97

[0036] From the foregoing comparisons, it is evident that for inventivealloys 1-7 the post-braze strength and conductivity is markedly improvedrelative to the alloy 15 fin. Self-corrosion as measured by weight lossafter 1 week in ASTM B 117 is comparable with alloy 15. Alloy 5represents a high Zn level that might be desired in some instances toprovide extra cathodic protection to the tube alloy. Zinc clearly has adetrimental influence on the conductivity and increases self-corrosionsomewhat. For the comparative alloys low in Fe and essentially free ofCu (alloys 9 and 10), while the post-braze conductivity is significantlyhigher than alloy 15, the post-braze strength is only comparable toalloy 15. Alloy 8 which had a high Fe content and was essentially freeof Cu also demonstrated high conductivity, but strength was comparableto alloy 15. Alloy 11 had a very high Zn content which, while itincreases post-braze UTS, (compare to alloy 5), resulted in a markedlylow conductivity. Nickel additions, such as used in alloy 12 and thehigh-Ni alloy 16 yield improved strength with minimal influence onconductivity. However, the self corrosion rate is notably increased.

[0037] Alloys 13 and 14 which are higher in Si content but substantiallyCu-free, also exhibited attractive combinations of post-braze propertiesin comparison to alloy 15. However the alloys of the present inventioncontain lower Si levels than those alloys and controlled Cu additionsfor strengthening without resulting in markedly decreased self-corrosionresistance.

[0038] Both alloys 6 and 7 demonstrated good conductivity and higherstrength than alloy 15 with acceptable grain size that would minimizesag and erosion tendencies. In addition, it is noted that thecombination of Zn and In in alloy 7 was effective in shifting thecorrosion potential of the fin to become more anodic with minimalinfluence on conductivity.

[0039] As noted previously, for ease of fabrication it can be desirableto include an intermediate anneal early in the fabrication sequence.Laboratory work on alloy 7 utilizing various process paths thatincorporated two intermediate anneals in the temperature range of320°-420° C. did not have any notable detrimental influence onpost-braze properties. If two intermediate anneals are to be used, it ispreferable that some cold work be imparted to the cast sheet prior tothe first anneal. Slightly lower post-braze properties are anticipatedif the first thermal treatment is imparted to the as-cast sheet prior tocold rolling, but these can still be acceptable properties for someapplications. As such the envisioned fabrication paths include routesthat have one or two intermediate anneals. The anneal temperatures arepreferably in the range of 320°-450° C. for preferably 1 to 8 hrs.

[0040] Control of post-braze grain size is important for hightemperature sag resistance. One factor that was found to be veryinfluential in controlling grain size is the amount of final coldreduction imparted after the last intermediate anneal. Smaller amountsof final cold reduction after the last intermediate anneal resulted incoarser post-braze grain sizes. In laboratory work it was found thatfinal cold reductions of as much as 44% reduction in thickness gavegrain sizes in excess of 500 microns for some combinations ofcomposition and fabrication sequences. As such, a final cold reductionof less than 50% is established. Reductions of less than about 35% arepreferable.

[0041] While preferred embodiments of the present invention weredescribed hereinabove, modifications and alterations of the presentinvention may be made without departing from the spirit and scope of thepresent invention. The scope of the present invention is defined in theappended claims and equivalents thereto.

What is claimed is:
 1. An aluminum alloy comprising: about 0.35-0.60 wt.% Si, about 1.8-2.6 wt. % Fe, about 0.02-0.30 wt. % Cu, about 0.40-0.70wt. % Mn, up to about 3.0 wt. % Zn, up to about 0.05 wt. % In, and up toabout 0.05 wt. % Ti, the balance aluminum, incidental elements andimpurities.
 2. The aluminum alloy of claim 1, which further contains upto about 0.2 wt. % Zr.
 3. The aluminum alloy of claim 1, which furthercontains up to about 0.3 wt. % Mg.
 4. The aluminum alloy of claim 2,which further contains up to about 0.3 wt. % Mg.
 5. The aluminum alloyof claim 1, which contains about 0.35-0.50 wt. % Si and about 1.8-2.4wt. % Fe.
 6. The aluminum alloy of claim 1, which contains about0.35-0.45 wt. % Si.
 7. The aluminum alloy of claim 1, which containsabout 0.10-0.25 wt. % Cu.
 8. The aluminum alloy of claim 1, whichcontains about 0.35-0.45 wt. % Si, about 1.8-2.4 wt. % Fe, about 0.4-0.7wt. % Mn, about 0.15-0.25 wt. % Cu, up to about 1.5 wt. % Zn and aboutup to 0.03 wt. % In.
 9. A process for making aluminum alloy finstockhaving improved combinations of post-braze tensile strength, electricalconductivity and self-corrosion resistance, said process comprising thesteps of: (a) continuously casting into sheet an alloy compositioncomprising: about 0.35-0.60 wt. % Si, about 1.8-2.6 wt. % Fe, about0.02-0.30 wt. % Cu, about 0.40-0.70 wt. % Mn, up to about 3.0 wt. % Zn,up to about 0.05 wt. % In; up to about 0.05 wt. % Ti and up to about 0.2wt. % Zr, the balance aluminum, incidental elements and impurities, saidcasting including a solidification rate of greater than about 200°C./sec. to substantially avoid formation of primary intermetallicsolidification compound; (b) rolling said sheet to an intermediateanneal gauge; (c) annealing the rolled sheet; and (d) cold rolling tofinal gauge.
 10. The process of claim 9, wherein the alloy containsabout 0.35-0.50 wt. % Si and about 1.8-2.4 wt. % Fe.
 11. The process ofclaim 9, wherein the alloy contains about 0.35-0.45 wt. % Si.
 12. Theprocess of claim 9, wherein the alloy contains about 0.10-0.25 wt. % Cu.13. The aluminum alloy of claim 9, wherein the alloy contains about0.35-0.45 wt. % Si, about 1.8-2.4 wt. % Fe, about 0.4-0.7 wt. % Mn,about 0.15-0.25 wt. % Cu, up to about 1.5 wt. % Zn and about up to 0.03wt. % In.
 14. The process of claim 9, wherein step (a) is performed witha twin roll caster under rapidly cooling casting conditions thatsubstantially avoid the formation of primary intermetallicsolidification compounds and produces a sheet of thickness of about2.0-10.0 mm.
 15. The process of claim 9, wherein step (b) includes aninitial intermediate thermal operation either at cast gauge or aftersome initial cold reduction.
 16. The process of claim 15, wherein saidintermediate thermal operation includes a 1-8 hour soak in a temperaturerange of about 320-450° C.
 17. The process of claim 9, wherein step (b)comprises cold rolling.
 18. The process of claim 9, wherein step (a) isperformed with a high speed sheet or belt caster that freezes from atleast one surface.
 19. The process of claim 18, wherein step (b)includes both hot or warm rolling and cold rolling.
 20. The process ofclaim 9, wherein said finstock has a post-braze ultimate tensilestrength of about 125 Mpa or higher and an electrical conductivity valueof about 48% IACS or greater.
 21. The process of claim 9, wherein step(c) is performed at one or more temperatures below about 450° C.
 22. Theprocess of claim 9, wherein step (d) produces less than or equal toabout a 50% reduction in sheet thickness.
 23. A heat exchangerfabricated from finstock made from an aluminum alloy consistingessentially of: about 0.35-0.60 wt. % Si, about 1.8-2.6 wt. % Fe, about0.02-0.30 wt. % Cu, about 0.40-0.70 wt. % Mn, up to about 3.0 wt. % Zn,up to about 0.05 wt. % In; up to about 0.05 wt. % Ti, up to about 0.2wt. % Zr, and up to about 0.3 wt. % Mg, the balance aluminum, incidentalelements and impurities.
 24. The heat exchanger of claim 23, wherein thealuminum alloy contains about 0.35-0.50 wt. % Si and about 1.8-2.4 wt. %Fe.
 25. The heat exchanger of claim 23, wherein the aluminum alloycontains about 0.35-0.45 wt. % Si.
 26. The heat exchanger of claim 23,wherein the aluminum alloy contains about 0.10-0.25 wt. % Cu.
 27. Theheat exchanger of claim 23, wherein the aluminum alloy contains about0.35-0.45 wt. % Si, about 1.8-2.4 wt. % Fe, about 0.4-0.7 wt. % Mn,about 0.10-0.25 wt. % Cu, up to about 1.5 wt. % Zn and about up to 0.03wt. % In.
 28. The heat exchanger of claim 23, wherein the aluminum alloyis of a gauge thickness about 75 microns or less.